1. Field of the Invention
The present invention relates to an ink-jet recording apparatus and a recording method, whereby a plurality of types of inks, which belong to the same color group but have different dye densities, are discharged onto a recording medium to perform recording, and resulting recorded articles.
2. Related Background Art
In the conventional ink-jet recording method, ink is discharged from a plurality of ink discharge ports, which are formed in a recording head, in accordance with data signals and the ink droplets are caused to adhere to a material to be recorded on such as paper. This recording method is employed for a printer, facsimile, and copier, for example.
In the aforesaid apparatus, there are methods available, including one using an electrothermal energy converter, wherein a heating device (electrothermal energy transducer) is provided, as a discharging means for discharging ink, in the vicinity of a discharge port, and an electrical signal is applied to the heating device to heat the ink locally to cause pressure change, thereby discharging the ink through the discharge port, and another method wherein an electromechanical transducer such as a piezoelectric device.
In this type of recording method, the recording control for medium tone according to a dot density control method, wherein the number of recording dots per unit area is controlled by a recording dot of a fixed size in order to represent the medium tone, or a dot diameter control method, wherein the size of the recording dot is controlled to represent the medium tone is carried out.
The latter dot diameter control method has restrictions because it requires complicated control; therefore, the former dot density control method is commonly used.
Further, the use of the electrothermal energy converter, which can be manufactured more easily and which permits higher density and accordingly higher resolution, as the ink discharging means, makes it difficult to control a pressure variation and also makes it impossible to change the diameter of the recording dot. For this reason, the dot density control method is used.
There is a systematic dither method as one of the typical binary techniques for representing medium tone used for the dot density control method, however, this method is disadvantageous in that the number of gradation levels is limited by a matrix size. To be specific, to increase the number of gradation levels, it is necessary to increase the matrix size, but increasing the matrix size causes a picture element of a recorded image comprised of a single matrix to grow larger with resultant lower resolution, thus posing problems. There is a conditioned decisive dither method such as an error diffusion method as another typical binary technique. This is a method, wherein a threshold value is changed, considering a peripheral picture element of an input picture element, while the aforesaid systematic dither method is an independent decisive dither method, wherein a threshold value, which is independent of an input picture element, is used for binarizing. The conditioned decisive dither method represented by this error diffusion method provides such advantages as good compatibility of gradation performance and resolution and minimized chances of a moire pattern occurring in a recorded image when an original image is a printed image, however, it also presented a problem in that grainy look in a lighter part of an image is more noticeable, leading to lower rating of the image quality. This problem was especially marked in a recording apparatus with a lower recording density.
To make the grainy look less conspicuous, a recording method has been proposed, wherein the conventional ink-jet recording apparatus is provided with two recording heads which discharge an ink of a low density or low dye density and an ink of a high density or high dye density; recording dots are formed with the ink of the low dye density for the light to medium tone parts of the image and the recording dots are formed with the ink of the high dye density for the medium to dark parts. When the inks of different dye densities is used, the density of the recorded image increases (the image becomes darker) as the dye density increases (becomes higher).
The use of a dark/light multi-value recording method, wherein a plurality of dark and light inks with different densities are used for a single color, improves the gradation of a highlighted part simply by upgrading from binary to ternary and decreases the dot graininess, resulting in a higher image quality. This is achieved by embedding the ink of a lower density (lighter) for the highlighted part, thereby eliminating the noise of a single dot.
This dark/light multi-value recording method, however, however, permits the elimination of the graininess by increasing the number of dye density levels of the dark and light inks. On the other hand, increasing the number of the density levels unavoidably increases the number of recording heads and ink tanks and also the size of a carriage carrying them, leading to an increased size of the whole apparatus. There are also limitation on the available number of different dark and light inks, two to four at the most. These restrictions are more marked especially in a color recording apparatus, and posed problems such as the impossibility of satisfactory reduction in the graininess in a highlighted part even when the method described above is used, and the reproduced gradation of an area, where the light ink is taken over by the dark ink, cannot be rendered linear when there is a significant difference in dot density between the dark and light color inks.
The following illustrates more problems which the applicant is aware of.
FIG. 36 shows a configuration diagram of a major section of the conventional color ink-jet recording apparatus of a serial print type which uses dark and light inks. Installed on a carriage with predetermined intervals are a recording head Kk, which discharges a dark black ink, a recording head Ku, which discharges a light black ink, a recording head Ck, which discharges a dark cyan ink, a recording head Cu, which discharges a light cyan ink, a recording head Mk, which discharges a dark magenta ink, a recording head Mu, which discharges a light magenta ink, a recording head Yk, which discharges a dark yellow ink, and a recording head Yu, which discharges a light yellow ink.
The inks for the individual recording heads are supplied from ink cartridges 12 corresponding to the individual colors. Further, the control signals to the recording heads are supplied via a flexible cable.
A material to be recorded on consisting of paper or a plastic thin plate is held by delivery rollers 21 via carrying rollers (not shown) and carried in the direction of the arrow as a carrying motor, which is not shown, runs. A carriage 23 is guided and supported by a guide shaft 22 and an encoder (not shown). The carriage is also shuttled by a carriage motor 25 along the guide shaft 22 mentioned above.
A heating device (electrothermal energy converter), which generates heat energy for discharging an ink is provided inside (liquid passage) the ink discharge port of the ink-jet unit described above. An image can be formed by driving the heating device in accordance with recording signals and the reading timing of the encoder to jet and deposit ink droplets onto a material to be recorded on in the order of the dark black, light black, dark cyan, light cyan, dark magenta, light magenta, dark yellow, and light yellow. A restoring unit with caps 26 is disposed in a home position HP of the carriage, which is selected and located outside a recording area, to maintain ink discharge stability.
The ink-jet recording apparatus, which employed dark and light inks as discussed above, however, requires that dark and light inks be prepared for each color. For example, if four colors are used, then at least eight different inks and ink cartridges must be prepared. In other words, there is a disadvantage in that a user must always keep eight different ink tanks. Accordingly, the apparatus itself unavoidably grows larger with complicated and troublesome change of the cartridges.
Furthermore, if there is a significant difference in dot density between the dark and light color inks, then the reproduced gradation cannot be rendered linear min the area where a light ink is taken over by a dark ink, frequently producing a pseudo-contour, or a change in graininess or tone of a recorded image takes place in an ink switching area, resulting in an unnatural image. To solve these problems, it is more desirable to increase the number of inks by using, for instance, low-density inks, medium-density inks, and high-density inks to perform the recording, however, this is difficult to carry out especially in a color recording apparatus because of the problems described above.
The present invention has been achieved in view of the problems discussed above, and it is an object thereof to provide an ink-jet recording apparatus and an ink-jet recording method which enable satisfactorily controlled graininess even with a fewer types of dark and light inks and permits recording with excellent gradation, and recorded articles.
The present invention for fulfilling the object mentioned above is an ink-jet recording apparatus, which forms an image by discharging inks on a recording medium by using a plurality of ink discharging means which are capable of discharging a plurality of inks with different densities, at least two of the ink discharging means discharging inks which differ in density and penetrability.
Further, according to the present invention, an ink-jet recording method is provided, wherein a plurality of inks with different densities are deposited on a recording medium to form an image, the image being formed by depositing inks on the recording medium, the inks having different densities and penetrability on the recording medium.
Still further, according to the present invention, a recorded article is provided, wherein an image has been formed on a recording medium by using a plurality of inks which differ in density and penetrability on a recording medium.
According to the present invention of the configuration described above, an image is formed by depositing inks, which differ in density and penetrability on a recording medium. This produces an image which is free of graininess and which exhibits good gradation.
It is another object of the present invention to solve the problems with the conventional apparatus described above and provide a small, inexpensive apparatus which features excellent gradation and resolution and which is capable of producing an image with an extremely good graininess, to minimize the number of the ink cartridges for supplying ink to the ink discharge means, and to permit easier operation.
To fulfill the above object, the ink-jet recording apparatus according to the present invention uses inks of at least two types of coloring materials, the ink of each coloring material being classified so that it has at least two different coloring material densities, has a plurality of ink discharge means for forming dots on a material to be recorded on by discharging the inks from the different ink discharge ports, which correspond to the plural inks, and controls the number of recording dots per unit area, which are discharged onto the material to be recorded on in accordance with an image signal, thereby permitting gradational recording, the ink cartridges, which hold the inks to be supplied to the ink discharge means, being grouped by the ink of the same type of coloring material.
Further, the ink-jet recording apparatus according to the present invention uses inks of different densities, has an ink discharge means, which discharges inks with different densities through different ink discharge ports corresponding to the inks of the plural densities to form dots on a material to be recorded on, and controls the number of recording dots per unit area in accordance with an image signal, thereby permitting gradational recording, the ink capacity of a cartridge, which supplies the ink to the ink discharge means, being different according to the predicted volume to be use of each ink.
The tanks holding inks, which are of the coloring materials of the same color but are different in density, are integrated into a single ink cartridge. Therefore, the ink cartridge can be replaced by each type of color. In addition, the capacities of the ink tanks are determined in accordance with the predicted volume of use of each ink; therefore, it is possible to prevent any ink tank from becoming empty earlier than others even when a plurality of ink tanks are combined to form the ink cartridge.